Fleas are repelled by the taste, smell and acidity of vinegar. However, vinegar only repels the insects, it does not kill them. Pet owners often give their pets vinegar as a dietary supplement or use it as a spray to help ward off the pests.
Using vinegar does have its drawbacks, however, as the smell is potent and unbearable for many people. Additionally, if pets ingest too much vinegar, it can be harmful to their health, but if they drink too little, it does nothing to repel fleas. While both white vinegar and apple cider vinegar work for this purpose, many pet owners prefer to use the latter, as dogs and cats who groom themselves prefer the slightly better taste of the apple cider vinegar.